This invention relates to automobile towing apparatus, and more particularly to apparatus of the type that can be mounted on the rear of a tow truck to provide an extensible and pivotal boom that carries a pair of spaced apart vehicle lifts for engaging portions, preferably the wheels, of a vehicle to be towed (referred to below for convenience as the "disabled vehicle" or simply "the vehicle").
Devices of this general type have been known for many years. Such developments are shown, for example, in U.S. Pat. Nos. 3,434,607 issued Mar. 25, 1969 to A. W. Nelson, 3,599,811 issued Aug. 17, 1971 to W. F. Watkins, 3,924,763 issued Dec. 9, 1975 to N. G. Pigeon (Canadian Pat. No. 986,155 issued Mar. 23, 1976) and 4,384,817 issued May 24, 1983 to F. H. Peterson.
Various practical difficulties have been experienced with these devices, however, especially when loading a disabled vehicle that is standing on sloping ground. Three sloping situations can typically arise and need to be accommodated, i.e. the disabled vehicle can have either a transverse, a forward or a rearward slope relative to the tow truck. Such situations often occur when the tow truck is required to load a disabled vehicle that is standing in a driveway that slopes either upwardly or downwardly from a street, or when the disabled vehicle is off a road on rough ground. Combinations of these slopes can also arise, as when the vehicle is in a ditch.